The field of the present invention is that of pyrotechnically controlled electrical switches.
Switches of this type are used for example to fire an explosive charge in a warhead or in systems for emergency opening of aircraft doors.
U.S. Pat. No. 4,339,638 describes a switch in which a piston is displaced by the action of gas pressure supplied by a pyrotechnic composition. This piston pushes a switch assembly that makes a number of electrical connections between the pins. The switch assembly is held in the disconnected position by a small collar sheared by the advance of the piston.
A switch of this kind suffers from several disadvantages. The shearing of the collar, the displacement of the two movable parts, and the establishment of contacts by deformation of conducting elements require considerable force and a non-negligible mass of pyrotechnic composition.
Displacement of several parts likewise involves relatively long response times, and the reproducibility of performance will be poor owing to the difficulty involved in reducing the coefficient of friction of one switch on another over the entire range of operating temperatures.
A switch of this kind is therefore absolutely unsuitable for weapons use, for example to fire a warhead with a response time on the order of a microsecond and a reliability on the order of 99%, and in a temperature range from -50.degree. C. to +60.degree. C.
German patent DE 2,755,322 describes an electrical switch in which the gases generated by burning a pyrotechnic composition cause displacement of a piston to bring it into contact with a stop.
The stop is connected electrically with a first electrical conductor and the body of the first piston is itself connected to a second conductor through the sheath of the switch.
The piston is held in its resting position by a pin that is sheared when the pressure rises, and is then held in its contact position with the stop by deformation, under the influence of the gas pressure, of a pan that surrounds the pyrotechnic composition and is displaced to push the piston.
A switch of this kind also requires a large amount of pyrotechnic composition to shear the pin and to move the piston and the pan.
In addition, the friction, which is difficult to reduce, increases the response time and reduces the reliability of the switch.
Further, the quality of the contact obtained can be random since it depends both on the quality of the contact between the pan and piston and the quality of the contact between the piston and the stop.
It is therefore possible for play to remain between the piston and stop when the pan is deformed and jammed against the wall of the switch body.
German utility models DE-U-7802837 and DE-U-7802836 describe pyrotechnically controlled switches in which the pressure generated by a gas-generating composition pushes a conducting plate through a ring having a conical shape.
The pressure of the gases deforms the plate, which then assumes a concave shape that allows it to make electrical contact between two conductors supported by the housing.
The friction of the periphery of the plate against the conical shape of the ring ensures an elastic grip between the plate and the conductors.
This type of switch also requires a large amount of pyrotechnic composition to move and deform the plate.
In addition, the quality of the electrical contact obtained depends on the rigidity of the fit of the plate against the conical surface of the ring and on the mechanical characteristics of the material of which the plate is made.
A switch of this kind therefore does not possess a sufficient degree of reliability.